Fast,common-path,switchable, achromatic phase-shifter for polarization interferometry

Abstract

A fast switchable phase-shifter using a pair of liquid-crystal devices with a switching angle of 60° is described. This phase-shifter can be placed in the common path traversed by the two orthogonally polarized beams emerging from a polarization interference microscope and used for digital phase measurements over a wide range of wavelengths. It can also be used in a stellar interferometer with orthogonally polarized beams for measurements of fringe visibility with white light.     

Optical Heterodyne Polarimeter for Studying Space-and Time-dependent State of Polarization of Light

Abstract

This paper describes an optical heterodyne polarimeter with a photodetector array by which the space- and time-dependent state of polarization (SOP) of light can be determined. Since no optical components for polarization control are used, the time response of the polarimeter is free from such components, but is basically limited to the frequency bandwidth of the photodetector array used. The signal and local oscillator beams are coherently photomixed to generate a beat photocurrent at every pixel of the photodetector array. The orthogonal linearly polarized two-frequency components of the local oscillator beam are superimposed with their respective counterpart orthogonally decomposed components of the elliptically polarized signal beam. The generated beat-photocurrent offers the significant physical parameters required for the determination of the space- and time-dependent SOP. The performance principle of the polarimeter is explained and confirmed experimentally.     

Device for magneto-optic signal detection with a small crystal prism

A device made of a birefringent crystal for signal detection of magneto-optic (MO) disks is presented. The light beam from a MO disk is separated into two orthogonally polarized components at the surface of a birefringent prism. After these two components are reflected by the top and the bottom surfaces of the prism inside, at the detector they become sufficiently separated from each other for discrete detection, even though the prism is small. A method for calculating the light intensities and the positions of focused beams in a birefringent prism and the results of a fundamental experiment are presented.     

Novelty filter that uses a bacteriorhodopsin film

We propose a new novelty optical filter that uses a bacteriorhodopsin film. This filter is based on the time-dependent nonlinear diffraction efficiency of real-time holograms recorded in the film. As soon as the signal beam carrying a pattern is diffracted by the polarization hologram recorded in the bacteriorhodopsin film, it begins to erase the hologram and suppresses the diffraction of the beam at the position of the stationary part of the pattern. This filter enhances only leading edges of moving patterns. In this system undesired scattered light, which is orthogonally polarized to the diffracted beam, is discriminated by a polarizer.     

Polarization changes at Lyot depolarizer output for different types of input beams

Lyot depolarizers are optical devices made of birefringent materials used for producing unpolarized beams from totally polarized incident light. The depolarization is produced for polychromatic input beams due to the different phase introduced by the Lyot depolarizer for each wavelength. The effect of this device on other types of incident fields is investigated. In particular two cases are analyzed: (i) monochromatic and nonuniformly polarized incident beams and (ii) incident light synthesized by superposition of two monochromatic orthogonally polarized beams with different wavelengths. In the last case, it is theoretically and experimentally shown that the Lyot depolarizer increases the degree of polarization instead of depolarizes.     

Acousto-optic imaging spectropolarimetry for remote sensing

We review the operating principles of noncollinear acousto-optic tunable filters (AOTF's), emphasizing the use of two orthogonally polarized beams for narrow-band imaging. Spectral characterization and spectral broadening measurements of commercially available AOTF's agree with theoretical predictions and reveal difficulties associated with imaging noncollimated light. An AOTF imaging spectropolarimeter for ground-based astronomy that uses CCD's has been constructed at NASA Goddard Space Flight Center. It uses a TeO(2) noncollinear AOTF and a simple optical relay assembly to produce side-by-side orthogonally polarized spectral images. We summarize the instrument design and initial performance tests. We include sample spectral images acquired at the Goddard Geophysical and Astronomical Observatory.     

Ferrodispersion: a promising candidate for an optical capacitor

A ferrodispersion, which comprises micrometer-sized magnetizable spheres dispersed in a ferrofluid, is shown to store retrievable optical energy. It is observed that when such dispersion is subjected to a transverse magnetic field and a linearly polarized monochromatic light with its electric vector perpendicular to the applied field is incident on it, then for a critical static magnetic field of moderate intensity the emerging light disappears. Upon removing the light and then switching off the field, again light of the same frequency and same state of polarization reappears. A time delay between emission of the light and switching off the field is observed. The statistical distribution of this delay is reported. Intensity of the retrieval signal is found to depend on the storage time. This effect is investigated. Storing and retrieval of optical energy will be useful for developing a magnetically tunable optical capacitor.     

Polarization separation of light beams at the interface of two mesophases

The features of reflection of the linearly polarized light beams at the interface between two regions of a nematic liquid crystal (LC) with the orthogonal director orientation have been analyzed. The relationship between light beam propagation in a LC material and polarization of laser radiation has been established. Rotation of the polarization plane of a light beam has been found for the radiation introduced through the free surface “LC—air” deformed due to the capillarity effect. The total internal reflection effect has been demonstrated experimentally together with the possibility for special separation of the orthogonally polarized light beams at the interface of two mesophases.     

Polarization phase-shifting interferometric technique for complete evaluation of birefringence

A full-field technique for simultaneous measurement of the magnitude of birefringence and its orientation is presented. This is achieved using a monolithic birefringence sensitive interferometer where the interference fringes carry the information of both the birefringence phase and the orientation of the fast axis of an optically transmissive anisotropic material placed at the output of the interferometer. The interferometer consists of a suitably polarization-masked cube beam splitter, orientated as in the Gates interferometer, which serves to generate a pair of orthogonally polarized and collinearly propagating light beams. Experimental results are obtained through an algorithm incorporating eight polarization phase-shifted interferograms.     

Single-pulse, Fourier-transform spectrometer having no moving parts

A Wollaston prism is used in the design of a polarizing Fourier-transform spectrometer with no moving parts. The effective path difference between orthogonally polarized components varies across the aperture of the instrument, forming an interferogram in the spatial rather than temporal domain. The use of a charge-integrating linear detector array permits the entire interferogram to be sampled simultaneously so that a full spectrum is obtained for a single pulse of light.     

Photocontrolled Hierarchical Self‐Assembly of Anisotropic Micropatterns of Nanofibers onto Isotropic Surfaces

Hierarchical self‐assembly is achieved using a visible light triggered photoreaction. A pro‐gelator, α‐diketone‐2,3‐didecyloxyanthracene, is photoconverted into a low molecular weight gelator, 2,3‐didecyloxyanthracene (DDOA), that self‐assembles into nanofibers. Spatial confinement and patterns of these nanofibers onto a surface are achieved by localizing initial nucleation with a focused laser and photogenerate subsequent fiber growth with the laser or gentler wide‐field irradiation. Remarkably, collective growth of nanofibers results in anisotropic micropatterns with orientation factors (OF) reaching 79%, resulting in collective emission of linearly polarized light. The OF, distance of collective growth and fiber density, are controlled by the photoirradiation conditions and the balance of interactions between DDOA aggregates and the glass surface. An unprecedented juxtaposition of orthogonally oriented nanofiber patterns on an isotropic surface is achieved with individual control of the fibers' main direction. In perspective, this photochemical method can be extended to a large variety of self‐assembling molecules.     

Self-recording phenomenon in the process of reconstruction from a highly efficient dynamic hologram on azo-dye-colored material with powerful Weigert's effect

The dynamic process of highly efficient holographic recording of two orthogonally circularly polarized plane light waves on the azo-dye-colored gelatin with powerful Weigert's effect is investigated. The investigation has shown that at some ratios of the intensities of the recording waves the self-recording phenomenon during the reconstruction process by the same actinic light (lambda=488.0 nm) is observed, and the diffractive efficiency for the probe light (lambda=632.8 nm) of an already fully recorded hologram increases again almost instantly after blocking one of the recording beams of low intensity. The maximum diffractive efficiency reaches 40%-45% in this case.     

Polarization-controlled multistage switch based on polarization-selective computer-generated holograms

We describe a polarization-controlled free-space optical multistage interconnection network based on polarization-selective computer-generated holograms: optical elements that are capable of imposing arbitrary, independent phase functions on horizontally and vertically polarized monochromatic light. We investigate the design of a novel nonblocking space-division photonic switch architecture. The multistage-switch architecture uses a fan-out stage, a single stage of 2 x 2 switching elements, and a fan-in stage. The architecture is compatible with several control strategies that use 1 x 2 and 2 x 2 polarization-controlled switches to route the input light beams. One application of the switch is in a passive optical network in which data is optically transmitted through the switch with a time-of-flight delay but without optical-to-electrical conversions at each stage. We have built and characterized a proof-of-principle 4 x 4 free-space switching network using three cascaded stages of arrayed birefringent computer-generated holographic elements. Data modulated at 20 MHz/channel were transmitted through the network to demonstrate transparent operation.     

Quantum phase measurements and non-classical polarization states of light

Abstract

In our paper we consider the non-classical behaviour of both the Hermitian (observable) Stokes parameters of light and the phase difference of two modes that describe the quantum polarization states of optical field. To characterize the degree of polarization of light we introduce a new quantity taking into account the quantum properties of different quantum states of two orthogonally polarized modes. The problem of determination of the phase difference in two modes of optical field for the quantum polarization states of light is discussed. To describe in general such a quantum field we introduce two pairs of the phase operators: the phase angles for the Stokes parameters of light in a three-dimensional picture of the Poincaré sphere. We also consider a special type of the eight-port polarization interferometer (polarimeter) for simultaneous homodyne detection of both the Stokes parameters of light and the polarization phase operators and their fluctuations as well. Using an anisotropic (spatioperiodic) Kerr-like nonlinear medium associated with the polarization interferometer we could generate and also observe the polarization-squeezed phase states of light. The fluctuations in the phase difference between two orthogonally polarized modes for these non-classical states are less than the fluctuations for light in coherent state.     

Detection of biological particles by the use of circular dichroism measurements improved by scattering theory

Light scattered from optically active spheres was theoretically analyzed for biodetection. The circularly polarized signal of near-forward scattering from circularly dichroic spheres was calculated. Both remote and point biodetection were considered. The analysis included the effect of a circular aperture and beam block at the detector. If the incident light is linearly polarized, a false signal would limit the sensitivity of the biodetector. If the incident light is randomly polarized, shot noise would limit the sensitivity. Suggested improvements to current techniques include a beam block, precise angular measurements, randomly polarized light, index-matching fluid, and larger apertures for large particles.     

Optical reversible programmable Boolean logic unit

Computing with reversibility is the only way to avoid dissipation of energy associated with bit erase. So, a reversible microprocessor is required for future computing. In this paper, a design of a simple all-optical reversible programmable processor is proposed using a polarizing beam splitter, liquid crystal-phase spatial light modulators, a half-wave plate, and plane mirrors. This circuit can perform 16 logical operations according to three programming inputs. Also, inputs can be easily recovered from the outputs. It is named the "reversible programmable Boolean logic unit (RPBLU)." The logic unit is the basic building block of many complex computational operations. Hence the design is important in sense. Two orthogonally polarized lights are defined here as two logical states, respectively.     

Development of a polarimetric optical fiber sensor for electronicmeasurement of high pressure

The theoretical understanding of the principle of pressure-induced polarization coupling is discussed, and the improved construction, operation, and temperature desensitization of a high-pressure (up to 100 MPa) fiber-optic sensor in two configurations is described. The sensor exploits the effect of polarization coupling between two orthogonally polarized eigenmodes of a highly birefringent, polarization-preserving optical fiber which serves as the sensing element. An idea of temperature desensitization of the sensor output signal is demonstrated. The requirements for an electronic measurement system based on the sensor are discussed, including indentification of the parametric and functional specifications and constraints of such a system     

Effects of optical feedback in a birefringence-Zeeman dual frequency laser at high optical feedback levels

Optical feedback effects are studied in a birefringence-Zeeman dual frequency laser at high optical feedback levels. The intensity modulation features of the two orthogonally polarized lights are investigated in both isotropic optical feedback (IOF) and polarized optical feedback (POF). In IOF, the intensities of both beams are modulated simultaneously, and four zones, i.e., the e-light zone, the o-light and e-light zone, the o-light zone, and the no-light zone, are formed in a period corresponding to a half laser wavelength displacement of the feedback mirror. In POF, the two orthogonally polarized lights will oscillate alternately. Strong mode competition can be observed, and it affects the phase difference between the two beams greatly. The theoretical analysis is presented, which is in good agreement with the experimental results. The potential use of the experimental results is also discussed.     

Highly efficient interconnection for use with a multistage optical switching network with orthogonally polarized data and address information

A novel optical interconnection is introduced for a multistage optical switching network that uses orthogonally polarized data and address information. The network is unique in that the data information is never regenerated and remains in optical form throughout (i.e., it is never converted into electrical information). This has two main consequences: (1) the bandwidth of the data is not restricted by electrical circuit considerations, and (2) the optical interconnections from one stage of the network to the next must be highly efficient. The interconnection meets several goals: high efficiency, preservation of cross polarization of data and address, low cross talk between polarizations, good manufacturability, resistance to misalignment caused by thermal expansion, and absence of significant aberrations. In addition, sychronization of the signals is maintained, as the optical path lengths for all routes through the system are equal.     

Wide angular aperture holograms in photorefractive crystals by the use of orthogonally polarized write and read beams

We demonstrate a method of simultaneous holographic recording and readout in photorefractive crystals that provides high write-read beam isolation and wide angular bandwidth. The method uses orthogonally polarized read and write beams and parallel tangent diffraction geometry near the equal curvature condition to provide spatially separable, orthogonally polarized diffracted output beams with high isolation and wide Bragg-matched angular bandwidth. The available angular bandwidth of this read-write technique is analyzed, simulated, and experimentally investigated. The measured angular bandwidth internal to the crystal is approximately 18° × 6° for our 45°-cut BaTiO(3) crystal, yet the entire hologram still demonstrates high Bragg selectivity. In contrast, traditional nonparallel-tangent geometries yield angular apertures of the order of 1° × 4°.